Process of tanning hides



July 30, 1929. w, SHAW 3,722,398

PROCESS OF TANNING HIDES Filed Jan. 23, 1928 Patented July so, was.

UNHTED STATES WILLIAM S. SHAW, OF BOYNJE CITY, MICHIGAN.

YROCESS F TANNING- HIDES.

Application filed January 23, 1928. Serial No. 248,873.

My invention relates to improvements in processes of tanning hides, and it consists 1n the steps hereinafter set forth.

An object of my invention is to provide a process of tanning hides which results in a saving of time and which can be carried out at a lower cost than the ordinary tanning process. I

A further object of 'my invention is to provide a tanning process which will leave the hides in better condition than that afforded by the ordinary process.

A further object is to provide a process of tanning hides in which certain tanning solutions are reconditioned so as to aid in accelerating the process, cutting down the labor of treating thehides, and in providing a product of superior, grade.

A further object is to prepare from spent tannin solution a reconditioned solution in which a portion of the non-tans are converted into tans, the reconditioned solution being suitable for use in the tanning of hides.

Other objects and advantages will appear in the following specification, and the novel features of the invention will be particularly pointed out in the appended claims.

My invention is illustrated inthe accompanying drawings, forming part of this application, in which Figure 1 isa diagrammatic plan view of a plurality of vats used in connection with my improved process,

Figure 2 is a diagrammatic View of a wheeling mechanism,

Figure 3 is a diagrammatic view of a treating tank, and

Figure 4 is a diagrammatic top plan view of a plurality of vats. 40 My improved process for tanning hides is preferably carried out substantially in three stages; that is to say, the first step is the treatment of the hides in a relatively weak tanning solution, which, as will be hereinafter pointed out, is a solution reconditioned after previous use. The secondstep is the wheeling or tumbling step, whereby the fibers of the hides are mechanically loosened so as to absorb tannin quickly, while the third step is a subsequent treatment with a relatively strong tannin solution.

Subsequent to the treatment in the third stage, the liquor of the solution is reconditioned in the manner hereinafter stated and may be used for treating the hides in the first stage, as stated.

- In carrying out my invention, I make use of a plurality of vats such as that shown in general at 1 in Figure 1. The tanning solution which is used in the first stage, I will designate solution A, while that in the last or third stage, I will designate solution B. Solution B is an ordinary, aqueous solution of tannin which may be extracted'from trees, shrubs, beans, barks, nuts or roots. For instance, I may use chestnut tannin, which is produced by boiling ground chestnut wood in Water for a suflicient time to extract the tannin from the wood. This solution consists of from 5 to 10% tannin and non-tans and from 90 to 95% water. The spent liquor used after treating hides in the third stage in the vats shown in the drawing at 2 is placed in amixing tank C. This solution is indicated generally at D. It is heated by a steam coil D E to approximately 195 F., which is the best temperature for causing the ready mixture of the ingredients which go to make up the reconditioned solution. The solution within the treating tank is tested by a barkometer or other suitable testing means for determining the percentage of tannin remaining in the tanning solution. For every 100 pounds of pure tannin in the solution coming from the vats 2 of the third stage, approximately 12 pounds of a reagent, such as sodium sulphite, is added for the purpose of converting a portion of the non-tans in the tanning solution, into tannin. In order to accomplish this reaction, the solution is agitated for about thrye e hours by an agitator, such as that shown at After thorough agitation, approximately 2 pounds of solution containing approximately 28% lactic acid or other suitable acid such as acetic or formic acid is added to the solution for each pounds of pure tannin in the solution, the purpose of the acid being to thicken the hides. This mixture is stirred continuously, and the temperature of ap- 100 proximately 195 F. is maintained so as to cause a thorough intermixture. Subsequently, an equal amount of sulphonated oil; that is to say, approximately 2 pounds for every 100 pounds of tannin, is added. This oil may 1 be a fish, vegetable, or mineral sulphonated oil. The purpose of the sulphonated oil is to lubricate the hide fibers and to permit a more ready penetration of tannin within the fibers. The solution, together with the added ingredients, is stirred for approximately 25 minutes, while the temperature is still maintained at'195 F. to cause the thorough intermixture.

I also add approximately 1 poundsof a. commercial solution of bisulphite of soda (35 to 36 Baum) for every 100 pounds of pure tannin, and this is stirred in with the mixture by the agitator for approximately 25 minutes.

The solution in the treating tank C is allowed to cool to approximately F. before it is used in the vats 1. The temperature of approximately 80 F. allows tannin to more readily penetrate the fibersof the hide, since, if the temperature is greater than the natural temperature of the hides, the solution would tend to be destructive.

In Figure 1, I have shown a plurality of vats indicated in general at I. The new hides are placed in these vats, and the tanning liquor, which has been reconditioned, I is placed in these vats. It will be seen that the fresh hides are first treated with the treated tanning solution. The usual time taken for treatment of the fresh hides in the vats I is aboutfifteen days.

The hides are removed and-placed in the wheeling or tumbling mechanism H shown in Figure 2. This mechanism is operated for approximately five minutes. The purpose of wheeling or tumbling the hides is to loosen the fibers to a sufficient extent so that when the hides are removed from the tumbling mechanism, they will be in a condition to rapidly absorb tannin which is carried in the tanning solution. The mechanism is simply a tumbling device in which the hides are carried around and dropped so as to bend and flex and thus open up the fibers.

From the mechanism, the hides are put into the vats 2, where they are allowed to remain for approximately twenty days. As stated above, the stronger tanning solution is placed in vats 2 and is then transferred to the treating tank C.

It will be seen from the description thus far that the hides are moved progressively from one set of vats to another while the tanning solution is transferred in the opposite direction, this tanning solution being reconditioned between the first'and last stages. The rate at which this transfer takes place will vary with conditions, but the arrangement is such that it is virtually a continuous process as distinguished from the older or ordinary methods, and tends to bring the hides more quickly into marketable condition.

I am aware that treated extracts have been used all through a tanning process, but without success, since the treated solutions are unsuitable for giving maximum weight to the leather. By the present process I add a harmless acid to the solution which thickens the leather in the preliminary or first stage of the tanning process, and as distinguished from the ordinary process, the last stage has the more concentrated tanning solution.

The reconditioning of the tanning solution and the opening up of the fibers by mechanical action permits the tanning to more readily enter the fibers and expedites the process. Furthermore, my process renders tans availa ble which would otherwise be useless in the solution and reduces the percentage of red tans which are harsh and unsuitable for younger hides.

I have provided a process which can be kept under absolute control and which produces a product having a maximum thickness and weight wit-l1 a desirable color and with the best grain texture.

I claim:

1. In a process of tanning hides which consist in subjecting the hides in successive stages to tanning solutions, said solutions having a greater proportion of tannin in each successive stage, the improvement which consists in adding a lubricating agent to the used solution from a later stage for use in an earlier stage to facilitate the penetration of tanning material in said earlier stage.

2. In a process as herein described, in which hides are treated in stages, first to a solution of relatively low tannin strength and later to a solution of relatively high tannin strength, the improvement which consists in converting a portion of the tannin from a spent solution which has been used in the later stage, and employing such converted solution in the earller stage;

' 3. In a process of tanning hides, in which the hides are treated in stages, first in a solution of relatively low tannin strength and subsequently in a solution of high tannin strength, the improvement which consists in preparing the solution of lowtannin strength by chemically treating the spent solution used in the later stage with a reagent which converts a portion of the non-tans into tans.

4. In a process of tanning hides, in which the hides are treated in stages, first in a solution of relatively low tannin strength and subsequently in a solution of high tannin strength, the'improvement which consists in preparing the solution of low tannin strength by treating the spent solution used in the later stage with a reagent which converts a portion of the non-tans into tans, and in adding a lubricating agent to said converted solution.

5. In a process of tanning hides, in which the hides are treated in stages, first in a solution of relatively low tannin strength and subsequently in a solution of high tannin strength, the improvement which consists in preparing the solution of low tannin strength by treating the spent solution usedin the later stage with a reagent which converts a portion of the non-tans into tans, and in add 'ing a hide-swelling agent to said converted solution.

1,7eaeee 6. In a process of tanning hides, which consists in subjecting the hides to tannin solutions in successive stages, the improvement which consists in adding a lubricating agent to the used solution from a later stage tor use in an earlier stage to facilitate the penetration of tannin in the earlier stage.

7. A process of tanning hides which consists in treating hides first in a relatively weak tannin solution, then loosening the fihers by mechanical action so as to render them comprising adding to the spent solution a sulphite solution which converts a portion of the non-tans into tans. t

10. A process of preparing a solution for tanning hides from a spent tannin solution,

comprising adding to the spent solution a,

chemical reagent which converts a portion ot the non-tans into tans, and adding thereto a hide-swelling acid.

11. A process of preparing a solution for tanning hides from a spent tannin solution,

comprising adding to the spent solution a chemical reagent which converts a portion of the non-tans into tans, and adding thereto a hide-lubricating agent. e

12. A process of preparing a solution for tanning hides from a spent tannin solution,

comprising adding to the spent solution a chemical reagent which converts a portion of the non-tans into tans, and adding thereto lactic acid and a sulphonated oil.

13. A tanning solution comprising converted non-tans, a hide-swelling acid and a sulphonated oil, and the unchanged residue of a chemical which has converted the nontans. a

14:- A tanning solution containing converted non-tans, and the unchanged residue of a chemical which has converted the nontans.

15. A tanning solution comprising con:

verted non-tans, lactic acid, a sulphonated oil, and the unchanged residue of a chemical.

which has converted the non-tans into tans.

16. A tanning solution containing converted non-tans, a hide-swelling agent, and the unchanged residue of a chemical which has converted the non-tans.

17. tanning solution containing con verted non-tans, a hide-lubricating agent, and the unchanged residue of a chemical which has converted the non-tans.

Signed at Chicago, in the county of Cook and State of Illinois, this 17th day of January, A. n. 1928.

wiLLiAM s. snaw, 

